Trajectory storage apparatus and method for surgical navigation systems

ABSTRACT

A method and apparatus for determining, calculating, and/or viewing a trajectory. The trajectory can be displayed on a display relative to image data of a patient. A user can use the system to determine relationships between two or more trajectories that have been determined. The relationships can be within two dimensional, three-dimensional, or four dimensional space. The relationships can include distance, angle, etc. The relationships can also be determined between real time trajectories and stored trajectories, or combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/177,739 filed on Jun. 21, 2002, now U.S. Pat. No. 6,920,347 issued onJul. 19, 2005, which is a continuation of U.S. patent application Ser.No. 09/545,092 filed on Apr. 7, 2000, now U.S. Pat. No. 6,535,756 issuedon Mar. 18, 2003. The disclosures of the above applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is directed generally to image-guided medicalprocedures, and more particularly, to systems and methods for thestorage and geometric measurement of instrument trajectories used inimage-based surgical guided navigation systems.

2. Description of the Related Art

Image based surgical techniques have been used with success in aidingphysicians for performing a wide variety of delicate surgicalprocedures. These procedures are typically used when the visualizationof a surgical tool could be obscured by a patient's anatomy, or when thesurgical tool is visible but the patient's anatomy may be difficult tovisualize in three dimensions. Such procedures include, for example,spinal implant placement, the alignment of broken bone fragments, andthe fixation of bone fractures. Prior art techniques to accuratelyposition a surgical instrument have included the use of x-ray images tolocalize its position. Through the repeated acquisition of x-ray imagesduring the procedure, real-time placement of the instrument relative tothe patient's anatomy can be displayed. More recently, virtualfluoroscopically-based surgical navigation systems have been employed totrack an instrument trajectory and superimpose its representation ontopre-acquired images without requiring x-rays to be repeatedly takenduring the actual surgical procedure.

In many situations, a surgeon would like to create a static visualreference using the real-time and generally instantaneous instrumenttrajectory displayed by the surgical navigation system as the instrumentprogresses in the general direction of a selected, desired path. Forexample, some procedures require the serial placement of severalimplants which must be placed in a precise relative geometry. Currently,the surgeon must reacquire a new set of images after each implant isplaced to properly determine the trajectory of the subsequent implant.This can be a time consuming process which increases the amount ofradiation exposure to the patient and operating room personnel.

Other situations may require the surgeon to make accurate geometricmeasurements of a patient's anatomy. For example, some surgicalprocedures require the precise removal of a specific amount of bonetaken in the shape of a wedge. In order to determine this amount, anangular measurement of the bone at the surgical site would assist inthis procedure. Another example would be in allowing the surgeon to makedistance measurement between bone implant sites to ensure proper implantplacement. In light of the foregoing, there is a need for the ability tosave surgical instrument trajectories and have the capability to performmeasurements thereon.

SUMMARY OF THE INVENTION

The present invention is directed generally to image guided medicalprocedures, and, particularly, to medical procedures involving thetracking of surgical instruments. More specifically, the presentinvention is directed to a device and method for storing instrumenttrajectories.

To achieve these objects and other advantages and in accordance with thepurposes of the invention, as embodied and broadly described herein, theinvention is directed to an apparatus and method for the storage oftrajectories and measurements which may be performed thereon for use inconjunction with image-guided surgical navigation systems.

In one aspect of the invention, an instrument trajectory is tracked inreal-time by a surgical navigation system. An icon representing thisreal-time trajectory is overlaid on one or more pre-acquired images ofthe patient. At the surgeon's command, the navigation system can storethe trajectory of the instrument and, if desired, create a static iconrepresenting the saved trajectory for display on each pre-acquiredimage. The icon representing the stored trajectory is simultaneouslydisplayed with the real-time trajectory's icon so the surgeon mayvisually compare them. The surgeon has the option of saving additionaltrajectories by reissuing the storage command.

In another aspect of the invention, the surgeon may measure anglesbetween pairs of any two trajectories. The angles are computed in theplane of the image, and are, therefore, computed separately for eachimage displayed. One option is to compute one or more angles between thereal-time trajectory and saved trajectories. These angles are preferablycomputed and displayed on each pre-acquired image. As the real-timetrajectory changes, the displayed values are preferably updated in eachimage in real-time. Another option is to measure one or more anglesbetween pairs of any two stored trajectories. As with the prior option,these angles could be computed and displayed separately for each image.

In yet another aspect of the invention, three dimensional distancesbetween pairs of points defined by one or more sets of two trajectoriescan be computed and displayed. One option is to measure the distancebetween the real-time trajectory and one or more saved trajectories.These measurements would be computed in real-time and updated on thedisplay as the real-time trajectory varies. Another option would becomputing and displaying distances between pairs of points defined byone or more sets of two user-selected stored trajectories. For either ofthese two options, the defined points may be represented by the tip ofeach trajectory as computed by the system, or may be defined by auser-selected extension projected from the trajectory's tip.

Preferably, the invention can overcome the problems of the prior art byproviding the surgeon with the visual reference and measurementinformation required for some surgical procedures.

Both the foregoing general description and the following detaileddescription are exemplary, and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand together with the description, serve to explain the principles ofthe invention.

FIG. 1 is a simplified block diagram of an embodiment of a system forthe storage and measurement of instrument trajectories in accordancewith the present invention.

FIG. 2 is a simplified side view of an embodiment of a system for use ininstrument trajectory storage and measurement in accordance with thepresent invention.

FIG. 3 is a block diagram of a process used to select, store, andcompute geometric properties of trajectories in accordance with thepresent invention.

FIG. 4 is an exemplary diagram of a display in accordance with anembodiment of the invention showing several stored instrumenttrajectories and the real-time trajectory superimposed on two images ofa patient's anatomy.

FIG. 5 is a simplified block diagram of an exemplary computer systemused in the surgical navigation system in accordance with one embodimentof the invention.

FIG. 6 is a block diagram of a process used compute the angle betweentwo trajectories in accordance with the present invention.

FIG. 7 is a is a block diagram of a process used compute the distancebetween the tips of two trajectories in accordance with the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

With reference to FIG. 1, there is shown schematically an apparatus inaccordance with the present invention for the storage of instrumenttrajectories. Image-based surgical navigation system 100 enables asurgeon to generate and display on monitor 115 the trajectory ofinstrument 125, which is preferably a surgical instrument configured inany known manner. Data representing one or more pre-acquired images 105is fed to navigation computer 110. Navigation computer 110 tracks theposition of instrument 125 in real-time utilizing detector 120. Computer110 then registers and displays the trajectory of instrument 125 withimages 105 in real-time. An icon representing the trajectory ofinstrument 125 is superimposed on the pre-acquired images 105 and shownon monitor 115. At the surgeon's command, the real-time trajectory ofinstrument 125 can be stored in computer 110. This command also createsa new static icon representing the trajectory of the instrument ondisplay 115 at the time the surgeon's command was issued. The surgeonhas the option of issuing additional commands, each one storing anreal-time trajectory and creating a new static icon for display bydefault. The surgeon can override this default and choose to not displayany static icon. The surgeon also has the option to perform a number ofgeometric measurements using the real-time and stored instrumenttrajectories. While the present invention described in more detail belowis exemplified by a fluoroscopic-based system, it is not limited to thedescribed embodiment and could be practiced with many different types ofnavigation systems.

FIG. 2 illustrates fluoroscopic image-based surgical navigation system200 according to the preferred embodiment of the present invention.System 200, described below in sufficient detail to allow anunderstanding and appreciation of the present invention, is explained ingreater detail in U.S. patent application Ser. No. 09/274,972 of DavidA. Simon et al., entitled “Navigation Guidance via Computer AssistedFluoroscopic Imaging,” filed on Mar. 23, 1999, now U.S. Pat. No.6,470,207 issued on Oct. 22, 2002, the entire disclosure of which ishereby incorporated by reference. However, it should be understood thatthe invention is not confined to use with this particular image guidedsurgical system.

Further referring to FIG. 2, an image-based surgical navigation system200 for acquiring and displaying x-ray images appropriate for a givensurgical procedure is shown. Pre-acquired images of patient 202 arecollected when a patient, lying on platform 205, is placed within C-arm212 of imaging device 210. The term “pre-acquired,” as used herein, doesnot imply any specified time sequence. Preferably, however, the imagesare taken at some time prior to when surgical navigation is performed.Usually, images are taken from two substantially orthogonal directions,such as anterior-posterior (A-P) and lateral, of the anatomy ofinterest. Imaging system 210 further includes x-ray source 214 and x-rayreceiving section 216 mounted on opposite sides of C-arm 212. Receivingsection 216 includes target tracking markers 222. System 210 furtherincludes C-arm control computer 226 which allows a physician to controlthe operation of imaging device 210. One implementation of imagingdevice 210 is the Model 9600 C-arm fluoroscope from OEC Medical Systems,Inc. of Salt Lake City, Utah, although tracking markers 222 aretypically not included in the Model 9600 C-arm fluoroscope and may haveto be added, however, the 9600 is otherwise structurally similar toimaging device 210. It is to be understood, however, that the inventionis not confined to the use of this type of imaging device.

Fluoroscopic images taken by imaging system 210 are transmitted tocomputer 226 where they may be forwarded to surgical navigation computer110. Computer 110 provides the ability to display the received imagesvia monitor 115. Other devices, for example, such as heads up displays,may also be used to display the images.

Further referring to FIG. 2, image-based surgical navigation system 100generally performs the real-time tracking of instrument 125, and, in thepreferred embodiment, also tracks the position of receiver section 216and reference frame 235. Detector 120 senses the presence of trackingmarkers on each object to be tracked. Detector 120 is coupled tocomputer 110 which is programmed with software modules that analyze thesignals transmitted by detector 120 to determine the position of eachobject in detector space. The manner in which the detector localizes theobject is known in the art, and is discussed, for example, in PCTApplication No. PCT/US95/12894 (Publication No. WO 96/11624) to Bucholz,the entire disclosure of which is incorporated by reference. Any type oftracking system known in the art can be used, including, by way ofexample only, acoustic, optical, LED/reflectors, electromagnetic, and/orother similar devices.

In general, instrument 125 is tracked by surgical navigation system 100using attached tracking markers 230 in order for its three-dimensionalposition to be determined in detector space. Computer 110 integratesthis information with the pre-acquired images of patient 202 to producea display which assists surgeon 270 when performing surgical procedures.An iconic representation of the trajectory of instrument 125 issimultaneously overlaid on the pre-acquired images of patient 202 anddisplayed on monitor 115. In this manner, surgeon 270 is able to see thetrajectory of the instrument relative to the patient's anatomy inreal-time.

Further referring to FIG. 2, the system according to the inventionpreferably has the ability to save the dynamic real-time trajectory ofinstrument 125. By issuing a command using foot-switch 280, for example,computer 110 receives a signal to store the real-time trajectory of theinstrument in the memory of computer 110. This “storage command” alsoinstructs computer 110 to generate a new static icon representing thesaved trajectory of the instrument, essentially “freezing” the icon atthe point when foot-switch 280 was closed. The static icon, along withthe icon representing the real-time trajectory of the instrument, can besimultaneously superimposed over the pre-acquired image. If multipleimages are being displayed, both static and real-time icons can besuperimposed on all of the displayed images. Other means of issuing thestorage command, such as, for example, through a graphical userinterface, may also be used. The surgeon also has the option of storingmultiple instrument trajectories. Each time a desired storage command isissued, the real-time trajectory of the instrument is stored in computer110 and a new static icon representing the stored trajectory isdisplayed on the pre-acquired image, or if more than one image is beingdisplayed, on all the pre-acquired images. These storage trajectoryfeatures are described in more detail below.

The system according to the invention preferably has the additionalcapability to measure angles between the real-time trajectory and one ormore of the stored trajectories. These “dynamic angles” are measured inthe image plane and are updated in real-time as the real-time trajectoryvaries. The computed values may then be displayed simultaneously withthe pre-acquired image. If more than one pre-acquired image is beingdisplayed, the angles for each image are preferably computed anddisplayed separately since they will be different for each image plane.Preferably, the system is configured to compute and display one or moreangles between pairs of stored trajectories selected by surgeon 270. Aswith the dynamic angle measurements, the angles between the storedtrajectories are computed in the image plane. They are preferablycalculated and displayed separately for each displayed image. Theseangle calculation features will be described in more detail below.

Furthermore, the system preferably also has the ability to computethree-dimensional distances between pairs of points defined by thereal-time trajectory and one or more stored trajectories selected bysurgeon 270. These “dynamic distance” values are displayed with theimage and vary as the instruments trajectory changes. The system alsopreferably has the ability to measure distances between pairs of pointsdefined by one or more pairs of stored trajectories and to display thisinformation with the image. For either distance measuring option, thepoint pairs above may be defined by the tips of the instrumenttrajectories, or they may be defined by extending the tips by auser-specified amount. Each of these options will be discussed in moredetail below. Unlike the angle calculation, the three-dimensionaldistance is not a planar measurement, as such it will not vary amongdifferent images. The distance parameters may be displayed separatelyfor each image, or, as in the preferred embodiment, may only bedisplayed in one location.

Image-based surgical navigation system 100 utilized in the preferredembodiment of the present invention may be the same as that used in theFluoroNav™ system, which utilizes the StealthStation® Treatment GuidancePlatform, both of which are available from Medtronic Sofamor Danek, Inc.

FIG. 3 shows flowchart 300 illustrating the preferred embodiment forstoring instrument trajectories and computing geometric quantities.System 100 tracks instrument 125 by detecting tracking markers 230 withdetector 120. Positions are computed in real-time in detector space bycomputer 110 and converted to frame space, which is a coordinate systemassociated with reference frame 235. The conversions used may be oneswhich are well known to those skilled in the art. The instrumenttrajectory is preferably tracked using two points, the tip and the hind,on instrument 125 which are obtained using known offsets from trackingmarkers 230 (step 305). The computation of the tip and hind positions isdescribed in more detail below. An icon representing the real-timetrajectory of instrument 125 may be superimposed on one or morepre-acquired images 105 (step 310). The real-time instrument trackingproceeds until the computer receives a storage command from the surgeon.In the preferred embodiment, this command is given by a signal initiatedby actuation of foot-switch 280. The surgeon may also use a graphicaluser interface, which is described in more detail below, running oncomputer 110 to issue a storage command (step 315). Upon receipt of thecommand, computer 110 stores the real-time trajectory of instrument 125by placing the positions of the instrument's tip and hind into memory(step 320). Computer 110 then displays an icon representing the storedtrajectory which may be superimposed, along with the real-timetrajectory, on the pre-acquired image. If more than one pre-acquiredimage is being displayed, both the stored and real-time icons can besuperimposed on all pre-acquired images (step 325).

After one or more trajectories are saved, surgeon 270 has the option ofcomputing several geometric measurements through exercising theappropriate commands on the computer's 110 graphic interface (step 330).The surgeon will then typically select which trajectories to perform themeasurements upon. Measurements may be performed between the real-timetrajectory and one or more user-selected stored trajectories.Alternatively, a number of measurements may also be made between pairsof user-selected stored trajectories which are chosen through the userinterface (step 335). Once the trajectory pairs are chosen, surgeon 270can select to have the angles and/or a distance measurements performed(step 340). The distance and angle calculations are described below inmore detail.

Finally, the values the surgeon chose to measure can be displayed onmonitor 115 simultaneously with the pre-acquired image and trajectoryicons. If the measurement being performed includes the real-timetrajectory, each displayed value can be updated in real-time as theposition of instrument 125 changes. If multiple pre-acquired images arebeing displayed, the angles can be displayed on each desired image.However, in the preferred embodiment, the distance values will typicallybe displayed in one location. (step 345).

FIG. 4 shows an exemplary display which is consistent with the preferredembodiment of the invention. Display 400 preferably includes of threeprimary default windows, 403 a-c. Two fluoroscopic images, 402 and 405,taken from different orientations of a patient, are shown in twowindows, 403 a-b, respectively. Control and status window 403 c providesthe surgeon with a set of software controls to vary the systemparameters and control the modes and functionalities of the FluoroNav™system. Note that image 405 is partially obscured by dialog box 410.

Further referring to FIG. 4, image 402 shows seven stored trajectories,415 a-g, and one real-time trajectory, 417. The hind points of eachstored trajectory are denoted with cross symbols 420 a-f. Note the crosssymbol of trajectory 415 f is not indicative of a hind point, but of anextension. Extensions will be described in more detail later. The hindpoint of real-time trajectory 417 is indicated by cross 422. Obviously,many other symbols other than a cross may be used to denote the hindpoint. Each trajectory, represented by a directional indicator such as aline, can be automatically assigned a different color and uniquenumerical label to easily identify it. Other types of directionalindicators may also be used, and different shapes, styles, sizes, andtextures can be employed to differentiate among the trajectories. Onlylabels 425 a-d, associated with trajectories 415 a, 415 d, 415 f, and415 g, respectively, are shown in window 403 a. The surgeon has theoption of not showing the label for any trajectory if desired. Thesurgeon also has the option of changing the default color or label textfor any trajectory through the controls contained in dialog box 410. Thefunctionality of dialog box 410 will be described in more detail below.

In certain situations, the surgeon may wish to know where the tip of theinstrument would be if it were extended along a path direction indicatedby its current trajectory. When software button 430 in window 403 c istoggled on, computer 110 will calculate and display the icon based uponthe previously set extension, as set by slider bar 435, and the currenttrajectory of the instrument. Toggling button 430 again will result inno extension being displayed. For example, if button 430 were previouslyactivated and slider 435 is set to 45 mm, selecting button 430 will setthe slider value to 0 mm. Activating it a second time will restore it to45 mm. The estimated position of the tip can be calculated by computer110 by projecting a fixed length beyond the instrument's tip in thedirection of the line formed by each instrument's tip and hind. As shownin FIG. 4, an exemplary extension 418 is shown in a different line stylefrom trajectory icon 415 g. This difference could also be a change incolor, type, and/or texture between extension 418 and current trajectory415 g. Computer 110 may vary the length of the extension as directed bythe surgeon through manipulating control slider 435 using computer 110'smouse or keyboard. The extension feature is described in greater detailin U.S. patent application Ser. No. 09/274,972, now U.S. Pat. No.6,470,207 issued on Oct. 22, 2002, which has been incorporated byreference. Although the look-ahead technique described above projectsthe graphical representation of the instrument into the image, there isno requirement that the instrument's graphical representation be in thespace of the image for the extension to be projected into the image. Inother words, for example, the surgeon may be holding instrument 125above the patient and outside the space of the image, so that therepresentation of the instrument does not appear in the images. However,it may still be desirable to project ahead a fixed length into the imageto facilitate planning of the procedure.

Further referring to FIG. 4, dialog box 410 allows the surgeon tocontrol various aspects of how trajectories and labels are displayed.Whenever the surgeon initiates a command to store a trajectory, a row isautomatically created in dialog box 410 and is identified by a numberappearing in column 440. The surgeon has the option of removing a savedtrajectory from display 403 a by selecting the appropriate button incolumn 445. The color or texture of a button in column 445 can indicatethe current icon display status.

Column 450 contains fields which indicate the text used in the labelsfor each stored trajectory. Computer 110 can select numerical values asdefaults, which are illustrated in labels 425 a-d, or the surgeon mayselect a custom label. This is accomplished by using computer 110'smouse to select the appropriate field of column 450 corresponding to thestored trajectory to be renamed. Once selected, the surgeon can usecomputer 110's keyboard to enter the desired text for the label.Furthermore, the label of each trajectory can be selectively displayedby activating the appropriate button in column 455 with the mouse. Thecolor or texture of the button can be used to indicate the displaystatus of the label for each stored trajectory. In this example, buttonscorresponding to trajectories 1, 5, 6, and 7 are in the “on” state whichresults only in labels 425 a-d being displayed in window 403 a.

Selection of one of the buttons in column 456 causes the default colorof the stored trajectory to be overridden by the user. Activation of theappropriate button displays a palette of colors from which one maychoose to color the respective icon.

The surgeon also has the ability to select the mode of display for eachicon. Selecting pull-down menu 458 allows the user to chose from one ofthree different display modes for each stored trajectory. The firstmode, “Hind→Tip,” creates an icon by drawing a line from the instrumentshind position to the instruments tip position as shown in icons 415 a-e.The second mode, “Tip→Ext.,” creates an icon by drawing a line from theinstrument's tip to the end of the extension. This mode is shown in icon415 f, which is displayed as a light colored cross to denote theextension. The third display mode, “Hind→Ext.,” draws a line from thehind of the instrument to the tip of the extension. This mode isexemplified in icon 415 g and extension 418. Column 457 indicates thedisplay mode associated with each stored trajectory.

Further referring to FIG. 4, the surgeon has the option to have computer110 compute and display measurements between selected trajectories.Button 459 commands computer 110 to display the measurements and allowsthe user to select which measurements to display. Pull-down menus 461,463 allow the user to choose the trajectories which will be used toperform the measurements. Note that the real-time instrument may be usedin conjunction with one or more pairs of any of the stored trajectories,or the measurements may be made against one or more pairs of any twosaved trajectories. Text fields 460, 462 indicate which trajectorieswill be used in the measurement. The results of the measurementcalculation will be displayed in windows 403 a-b. In FIG. 4, the planarangle between real-time trajectory 417 and stored trajectory 415 a isshown at 470 in window 403 b and 480 in window 403 a. The differencebetween values 470 and 480 is due to the different planar geometriesassociated with images 402 and 405.

Referring to FIG. 5, components and modules of a computer system 110used to perform various processes of the present invention aredescribed. Although a STEALTH STATION® image guided system manufacturedby Medtronic Sofamor Danek has been identified, it will be appreciatedthat the present invention may be utilized with other types of computersystems. One aspect of the computer system 110 includes a graphical userinterface system operating in conjunction with a display screen of adisplay monitor 115. The graphical user interface system is preferablyimplemented in conjunction with operating system 515 running computer110 for displaying and managing the display objects of the system. Thegraphical user interface is implemented as part of the computer system110 to receive input data and commands from a conventional keyboard 520and mouse 525. Foot-switch 280 is also configured to enable the user toinitiate the storage of instrument 125's real-time trajectory. Forsimplicity of the drawings and explanation, many components of aconventional computer system have not been illustrated such as addressbuffers, memory buffers, and other standard control circuits becausethese elements are well known in the art and a detailed descriptionthereof is not necessary for understanding the present invention.

A computer program used to implement the various steps of the presentinvention is generally located in memory unit 500, and the processes ofthe present invention are carried out through the use of a centralprocessing unit (CPU) 505. Those skilled in the art will appreciate thatthe memory unit 500 is representative of both read-only memory andrandom access memory. The memory unit also contains a database 550 thatstores data, for example, image data and tables, including suchinformation as stored instrument tip and hind positions, extensionvalues, and geometric transform parameters, used in conjunction with thepresent invention. CPU 505, in combination with the computer softwarecomprising operating system 515, scanning software module 530, trackingsoftware module 535, calibration software module 540, and displaysoftware module 545, controls the operations and processes of computersystem 110. The processes implemented by CPU 505 may be communicated aselectrical signals along bus 560 to an I/O interface 570 and a videointerface 575.

Scanning software module 530 performs the processes associated withcreating a coordinate reference system and reference images for use inconnection with the present invention and are known to those skilled inthe art. Tracking software module 535 performs the processes necessaryfor tracking objects in an image guided system as described herein andare known to those skilled in the art. Calibration software module 640computes the geometric transform which corrects for image distortionsand registers the images to the anatomical reference frame 235, and thusthe patient's anatomy.

Display software module 545 applies, and if desired, computes theoffsets between the guide tracking markers 230 and the tip and hind ofthe instrument in order generate an icon representing the trajectory ofthe instrument for superposition over the images. For instruments withfixed lengths and angulations, these offsets can be measured once andstored in database 550. The user would then select from a list ofinstruments, the one being used in the procedure so the proper offsetsare applied by display software module 545. For instruments withvariable lengths and angulations, the offsets could be measured manuallyand entered via keyboard 520, or measured using the navigation system100 in conjunction a tracked pointer or tracked registration jig (notshown). If a tracked pointer is used, the user will touch the tip andtail of the instrument while it is being tracked. The offsets arecomputed by display software module 545 and stored for later use.Similarly, if a tracked registration jig is used, the instrument isplaced within the jig while it is being tracked. The jig will measurethe extremities of the instrument and display software module 545 willagain compute the offsets and store them for later use in database 550.

Pre-acquired image data 105 can be fed directly into computer 110digitally through I/O interface 570, or may be supplied as video datathrough video interface 575. In addition, items shown as stored inmemory can also be stored, at least partially, on hard disk 580 ifmemory resources are limited. Furthermore, while not explicitly shown,image data may also be supplied over a network, through a mass storagedevice such as a hard drive, optical disks, tape drives, or any othertype of data transfer and storage devices which are known in the art.

FIG. 6 shows a block diagram illustrating a method for calculating aplanar angle between two trajectories for the preferred embodiment.After surgeon 270 selects the trajectories using pull-down menus 461,463as described above, the tip and the hind positions of each trajectoryare projected into the image plane. Since x-ray receiving section 216 istracked by navigation system 100 utilizing tracking markers 222, thecoordinates of the image plane are well defined. Using the tip, hind,and image plane coordinates, the projection is performed usingtechniques well known to those skilled in the art (610). A first linesegment is constructed by connecting the projected tip and hind pointscorresponding to the first trajectory computed above (step 620). In thesame manner, a second line segment is constructed utilizing theprojected points of the second trajectory (step 630). The anglecorresponding to the intersections of the two aforementioned linesegments can then be computed by techniques known to those skilled inthe art (step 640).

FIG. 7 shows a block diagram illustrating a method of the preferredembodiment for calculating a distance between points in space as definedby two trajectories. After surgeon 270 selects two trajectories usingpull-down menus 461, 463 in the manner described above, a first point isdetermined using the three-dimensional tip position of the firsttrajectory as computed by navigation system 100. If a “look-ahead”extension is associated with the first trajectory, it is added to thetip position (step 710). A second point associated with the secondtrajectory is computed in the same manner as described for step 710(step 720). The distance may then be computed using thethree-dimensional coordinates of the first and second points by astandard Euclidean distance formula which is well known in the art.

The foregoing description is presented for purposes of illustration andexplanation. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed, and modifications of variationsare possible in light of the above teachings or may be acquired frompractice of the invention. The principles of the invention and itspractical application enable one skilled in the art to utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated.

For example, pre-acquired images obtained from different modalities maybe used in place of those produced by the C-arm fluoroscope x-rayimager. Such modalities include, by way of example only, computertomography, ultrasound, PET, or magnetic resonance imaging.

1. A method for determining a relative location of at least twotrajectories, the method comprising: providing image data of a patientin a first plane; tracking a three-dimensional trajectory of an object;determining, with a surgical navigation system, a position of a firstrepresentation of a first trajectory of the object relative to theprovided image data of the patient; determining, with the surgicalnavigation system, a position of a second trajectory of the objectrelative to the image data of the patient; and storing the firsttrajectory or the second trajectory.
 2. The method of claim 1, furthercomprising: displaying the provided image data; forming a representationof the determined position of the first trajectory of the object; andsuperimposing the formed representation of the first trajectory of theobject on the displayed image data.
 3. The method of claim 2, furthercomprising changing the formed representation to a second formedrepresentation and superimposing the second formed representation on thedisplayed image data.
 4. The method of claim 1 further comprising:selecting the first and second trajectory; projecting the firsttrajectory into a plane of the image data to form a first set ofprojected points; projecting the second trajectory into the plane of theimage data to form a second set of projected points; calculating a firstsegment connecting the first set of projected points; calculating asecond segment connecting the second set of projected points; computingan angle between the first and second segments in the plane of the imagedata; and displaying the computed angle.
 5. The method of claim 4further comprising using the displayed computed angle for performing atleast one of bone fragment alignment, bone fracture fixation, implantplacement, bone removal and spinal implant placement.
 6. The method ofclaim 1, further comprising storing both of the first trajectory and thesecond trajectory.
 7. The method of claim 6, further comprising:determining which of at least one of the determined first trajectory orthe determined second trajectory is a real-time trajectory; wherein thedetermined real time trajectory is stored contemporaneously with thetracking of the three-dimensional trajectory of the object.
 8. Themethod of claim 1, wherein providing image data of a patient includesproviding at least one of one-dimensional image data, two-dimensionalimage data, three-dimensional image data, four-dimensional image data,or combinations thereof.
 9. The method of claim 1, wherein providingimage data of the patient in a first plane includes providing image dataof a patient in at least a first plane and a second plane.
 10. Themethod of claim 9, wherein tracking a three-dimensional trajectory of anobject includes tracking the three-dimensional trajectory of the objectrelative to at least the first plane or the second plane.
 11. The methodof claim 9, wherein providing image data of a patient in the first planeincludes providing image data of a patient in at least one of ananterior to posterior plane, a lateral plane, a superior to inferiorplane, a coronal plane, a sagittal plane, or combinations thereof. 12.The method of claim 9, wherein providing image data includes providingimage data from an x-ray, a fluoroscope, a MRI, a PET scanner, computertopography, ultrasound scanners, or combinations thereof.
 13. The methodof claim 1, wherein providing image data of a patient in a first planeincludes obtaining image data of the patient in a first plane prior tothe tracking of the three-dimensional trajectory of the object.
 14. Themethod of claim 1, wherein storing at least one of the first trajectory,the second trajectory, or combinations thereof, includes storing adynamic real-time trajectory of the object.
 15. The method of claim 1,wherein storing at least one of the first trajectory, the secondtrajectory, or combinations thereof, includes storing a firsttrajectory; wherein determining a position of a second trajectory of theobject relative to the image data of the patient includes determining areal-time trajectory; determining a distance between the stored firsttrajectory and the determined position of the second trajectory;displaying the determined distance.
 16. The method of claim 15, furthercomprising: updating the distance in real-time while trackingthree-dimensional trajectory of the object.
 17. The method of claim 15,further comprising: projecting the first stored trajectory onto a planeof the image data; projecting the determined position of the secondtrajectory in real-time on the image data; computing a distance betweenthe first stored trajectory and the second determined position of thesecond trajectory; and displaying the determined distance.
 18. Themethod of claim 1, further comprising determining a distance between thefirst stored trajectory and the second stored trajectory.
 19. The methodof claim 18, wherein determining the distance between the first storedtrajectory and the second stored trajectory includes determining adistance in three-dimensional space.
 20. The method of claim 1, furthercomprising determining an extension of at least one of the firsttrajectory, the second trajectory, or combinations thereof.
 21. Themethod of claim 20, wherein determining the extension includesdetermining a projected position of the object based upon the determinedfirst trajectory, the determined second trajectory, or combinationsthereof.
 22. The method of claim 20, further comprising: selectivelydisplaying the determined extension.
 23. The method of claim 1, furthercomprising providing the object to have a tip and a hind: wherein thefirst trajectory, the second trajectory, or combinations thereof includea trajectory of at least one of the hind or the tip.
 24. An apparatusfor determining a trajectory of at least one object during a surgicalprocedure, said apparatus comprising: a tracking system operable totrack a three-dimensional position of the object; a computer processorin communication with said tracking system; a memory in communicationwith said computer processor, said memory storing: image data of apatient; instructions that when executed by said computer processor,track the trajectory of the object, store a first tracked trajectoryinto memory upon receiving a storage command, generate representationsof a second tracked trajectory and the first stored trajectory, andsuperimpose the representations onto the image data; and a displayoperable to display the superimposed representations onto the imagedata.
 25. The apparatus of claim 24 further comprising computerinstructions that when executed by the computer processor: selects afirst and a second trajectory from memory; projects the first trajectoryinto the image data to form a first set of projected points; projectsthe second trajectory into the image data to form a second set ofprojected points; calculates a first segment connecting the first set ofprojected points; calculates a second segment connecting the second setof projected points; computes an angle between the first and secondsegments; and displays the computed angle.
 26. The apparatus of claim25, wherein the image data is two-dimensional image data of the patientand defines a plane through the patient: wherein the computed anglebetween the first segment and the second segment is within the planedefined by the image data.
 27. The apparatus of claim 25, wherein theimage data is two-dimensional image data that defines the plane throughthe patient: the computed angle between the first and second segmentsincludes an angle defined relative to the plane.
 28. The apparatus ofclaim 25, wherein said tracking system is operable to track athree-dimensional position of the object in real-time: wherein thecomputer instructions when executed by the computer processor projectsthe real-time trajectory into the image stated to form a third set ofprojected points; that completes a third segment connecting the thirdset of projected points; computes an angle between at least the firstsegment or the second segment relative to the third segment.
 29. Theapparatus of claim 24 further comprising computer instructions that whenexecuted by the computer processor: selects a first and a secondtrajectory from memory; computes a first point based on a tip positionof the first trajectory; computes a second point based on a tip positionof the second trajectory; computes a distance in three-dimensional spacebetween the first point and the second point; and displays the computeddistance.
 30. The apparatus of claim 29, wherein the tracking system isoperable to track a real-time three-dimensional position of the object;wherein the generated representations of the second tracked trajectoryis the representation of a real-time tracking of the object relative tothe first stored trajectory; wherein computes a distance inthree-dimensional space between the first point and the second pointincludes a dynamic distance between the first point and the secondpoint.
 31. The apparatus of claim 30, wherein the instructions executedby the computer processor are operable to change the computed distancein three-dimensional space between the first point and the second pointin real time.
 32. The apparatus of claim 29, wherein the image data isthree-dimensional image data of the patient: wherein displays thecomputed distance on the display relative to the three-dimensional imagedata.
 33. The apparatus of claim 29, wherein the image data of thepatient is two-dimensional image data: wherein the display of thecomputed distance is a distance displayed relative to the plane definedby the two-dimensional data.
 34. The apparatus of claim 33, wherein thedisplayed computed distance includes at least one of the computed firstpoint or computed second point that is not in the plane defined by theimage data.
 35. The apparatus as defined in claim 29 further comprisingcomputer instructions that when executed by the computer processor:extends at least one of a path of the first trajectory and computes afirst extended point; extends a path of the second trajectory andcomputes a second extended point, or combinations thereof; computes adistance in three-dimensional space between at least one of the firstextended point, the second extended point, the first point, the secondpoint, or combinations thereof; and displays the computed distance. 36.The apparatus of claim 35, wherein the computer instructions whenexecuted by the computer extends a path of both the first trajectory andthe second trajectory and computes a first extended point from the firsttrajectory and computes a second extended point from the secondtrajectory: computes a distance in three-dimensional space between thefirst extended point and the second extended point.
 37. The apparatus ofclaim 35, wherein the computed distance is displayed relative to athree-dimensional image data of the patient.
 38. The apparatus of claim35, wherein the computed distance is displayed relative totwo-dimensional image date of the patient.
 39. The apparatus of claim35, wherein the second trajectory includes a substantially real-timetracked three-dimensional trajectory of the object: wherein the computeddistance in three-dimensional space is a dynamic distance between thesecond extended point and the first extended point.
 40. The apparatus ofclaim 35, wherein the image data of the patient is two-dimensional imagedata: wherein the first extended point relies on a first plane and thesecond extended point relies on a second plane; wherein the computeddistance in three-dimensional space is between the first plane and thesecond plane relative to the plane defined by the two-dimensional imagedata.
 41. The apparatus of claim 35, wherein the computer instructionswhen executed by the computer displays the first extended point relativeto the first trajectory or displays the second extended points relativeto the second trajectory on the display.
 42. The apparatus of claim 41,further comprising: a toggle portion; wherein the toggle portion isoperable to be manipulated by a user to selectively display the firstextended point, the second extended point, or combinations thereof. 43.The apparatus of claim 24, wherein the object includes at least one of atip, a hind, or combinations thereof: wherein the first trackedtrajectory, the second tracked trajectory, or combinations thereof is atracked trajectory of at least one of the tip, the hind, or combinationsthereof.
 44. The apparatus of claim 43, further comprising a selectionportion: wherein the selected portion is operable to be manipulated by auser to select the display of the first trajectory relative to the tip,the first trajectory of the hind, the second trajectory at the tip, andthe second trajectory of the hind, or combinations thereof.
 45. Theapparatus of claim 44, wherein the display is operable to display theselected trajectory.
 46. The apparatus of claim 24, further comprising:a calibration jig: wherein the object is operable to be positioned inthe calibration jig; wherein the tracking system is operable to trackthe calibration jig; wherein the instructions that when executed by theprocessor further tracks the calibration jig, determines a size of theobject, determines a position of a tip, determines a position of a hind,or combinations thereof.
 47. An apparatus for storing a trajectory of atleast one object during a surgical procedure, said apparatus comprising:a computer processor in communication with a tracking system; a memorysystem in communication with said computer processor, said memorystoring: image data of a patient from at least two planes; andinstructions that when executed by said computer processor: track thetrajectory of the object, store the trajectory into the memory systemupon receiving a storage command, generate representations of thetracked trajectory and the stored trajectory, superimpose therepresentations onto at least one of the planes of the image data,select a first and a second trajectory, at least one of compute adistance in three-dimensional space between the first and secondtrajectories, compute an angle between the first and secondtrajectories, or combinations thereof; and a display in communicationwith the computer processor operable to display at least one of thesuperimposed representations, the computed distance, the computed angleonto the image data, or combinations thereof.
 48. The apparatus of claim47, wherein said first and said second trajectories are from memory. 49.The apparatus of claim 47, wherein at least one of said first and saidsecond trajectories are real time trajectories.
 50. The apparatus ofclaim 47 further comprising computer instructions that when executed bythe computer processor: projects the first trajectory into the imagedata to form a first set of projected points; projects the secondtrajectory into the image data to form a second set of projected points;calculates a first segment connecting the first set of projected points;calculates a second segment connecting the second set of projectedpoints; computes the angle between the first and second segments; anddisplays the computed angle.
 51. The apparatus of claim 47, wherein thecomputed angle between the first segment and the second segment iswithin at least one of the planes defined by the image data.
 52. Theapparatus of claim 47, wherein the computed angle between the first andsecond trajectories includes an angle defined relative to at least oneof the planes of the image data.
 53. The apparatus of claim 47 whereinthe object has a tip and wherein computer instructions that whenexecuted by the computer processor: selects a first and a secondtrajectory from memory; computes a first point based on a tip positionof the first trajectory; computes a second point based on a tip positionof the second trajectory; computes a distance in three-dimensional spacebetween the first point and the second point; and displays the computeddistance.
 54. The apparatus of claim 53, wherein the instructionsexecuted by the computer processor are operable to change the computeddistance in three-dimensional space between the first point and thesecond point in real time.
 55. The apparatus of claim 47, wherein thecomputed three-dimensional distance is between the two planes.
 56. Theapparatus of claim 47, wherein the image data is three-dimensional imagedata of the patient: wherein displays the computed distance on thedisplay relative to the three-dimensional image data.
 57. The apparatusof claim 47, wherein the displayed computed distance includes at leastone of the computed first point or computed second point that is not inthe plane defined by the image data.
 58. The apparatus of claim 57,wherein the displayed computed distance includes one of the computedfirst point or computed second point is in the plane defined by theimage data and the other of the computed first point or computed secondpoint is not in the plane defined by the image data.
 59. The apparatusas defined in claim 47 further comprising computer instructions thatwhen executed by the computer processor: extends at least one of a pathof the first trajectory and computes a first extended point, extends apath of the second trajectory and computes a second extended point, orcombinations thereof; computes a distance in three-dimensional spacebetween at least one of the first extended point, the second extendedpoint, the first point, the second point, or combinations thereof; anddisplays the computed distance.
 60. The apparatus of claim 59, whereinthe computer instructions when executed by the computer extends a pathof both the first trajectory and the second trajectory and computes afirst extended point from the first trajectory and computes a secondextended point from the second trajectory: and computes a distance inthree-dimensional space between the first extended point and the secondextended point.
 61. The apparatus of claim 59, wherein the firstextended point lies on a first plane and the second extended point lieson a second plane; wherein the computed distance in three-dimensionalspace is between the first plane and the second plane relative to theplane defined by the two-dimensional image data.
 62. The apparatus ofclaim 59, wherein the computer instructions when executed by thecomputer displays the first extended point relative to the firsttrajectory or displays the second extended points relative to the secondtrajectory on the display.
 63. The apparatus of claim 62, furthercomprising: a toggle portion; wherein the toggle portion is operable tobe manipulated by a user to selectively display the first extendedpoint, the second extended point, or combinations thereof.
 64. Theapparatus of claim 47, wherein the computed distance inthree-dimensional space is a dynamic distance between the secondextended point and the first extended point.
 65. The apparatus of claim47, wherein the object includes at least one of a tip, a hind, orcombinations thereof: wherein the first tracked trajectory, the secondtracked trajectory, or combinations thereof is a tracked trajectory ofat least one of the tip, the hind, or combinations thereof.
 66. Theapparatus of claim 65, further comprising: a selection portion; whereinthe selected portion is operable to be manipulated by a user to selectthe display of the first trajectory relative to the tip, the firsttrajectory of the hind, the second trajectory at the tip, and the secondtrajectory of the hind, or combinations thereof.
 67. The apparatus ofclaim 66, wherein the display is operable to display the selectedtrajectory.
 68. The apparatus of claim 47, further comprising: acalibration jig; wherein the object is operable to be positioned in thecalibration jig; wherein the tracking system is operable to track thecalibration jig; wherein the instructions when executed by the processorfurther tracks the calibration jig, determines a size of the object,determines a position of a tip, determines a position of a hind, orcombinations thereof.